Dual-polarization fiber-optic gyroscope for realizing sensitivity enhancement and relative intensity noise suppression

Abstract

The invention discloses a dual-polarization fiber-optic gyroscope for realizing sensitivity enhancement and relative intensity noise suppression, which belongs to the technical field of fiber-optic gyroscopes and is characterized in that orthogonal polarized light propagating in a polarization-maintaining fiber ring presents complementary response with equal magnitude and opposite symbols to the same rotating speed through dual-polarization modulation of the gyroscope; sensitivity enhancement is realized by using a difference algorithm; and meanwhile, the same and synchronous relative intensity noise in the two polarization states is effectively suppressed by adopting a noise subtraction method. Light emitted by the light source is processed by the polarizer, the circulator and other devices, dual-polarization modulation is completed in the modulator, sensing is performed in the optical fiber ring, finally, the light is converted into electric signals through the photoelectric detector, and signal processing is achieved in the FPGA. The performance of the gyroscope can be effectively improved, and sensitivity enhancement and relative intensity noise suppression are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of fiber optic gyroscopes, and in particular to a dual-polarization fiber optic gyroscope that realizes sensitivity enhancement and relative intensity noise suppression. Background Art

[0002] A fiber optic gyroscope is a high-performance all-solid-state inertial sensor based on the Sagnac effect, with technical advantages such as high precision, long lifespan, and fast startup, and is applied in various fields including land, sea, air, and space. Researchers from various countries have conducted extensive research on integrated gyroscopes and proposed a variety of different miniaturized gyroscope structures.

[0003] As the core of an inertial system, a gyroscope is used to accurately measure the angular velocity of a carrier. An interferometric fiber optic gyroscope (IFOG) has been widely applied in many fields due to its advantages such as no moving parts, wide precision coverage range, large dynamic range, and high reliability. However, with the development of technology, higher requirements are put forward for the performance of IFOG in various application scenarios. For example, in aerospace navigation, a tiny angular velocity measurement error may cause the deviation of the flight vehicle's orbit; in an inertial inclinometer for oil exploration, noise interference will affect the measurement accuracy, thereby affecting the mining efficiency and cost. Existing IFOG technologies have deficiencies in sensitivity and noise suppression, which limit their application in scenarios with high-precision and high-stability requirements. Traditional IFOGs are difficult to simultaneously achieve high sensitivity and low noise and cannot meet the growing market demand. Therefore, it is of great significance to develop new IFOG technologies. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a dual-polarization fiber optic gyroscope that realizes sensitivity enhancement and relative intensity noise suppression, aiming to achieve optimization in terms of sensitivity and noise suppression and improve the performance of the fiber optic gyroscope.

[0005] To solve the above technical problem, the technical solution adopted by the present invention is: a dual-polarization fiber optic gyroscope that realizes sensitivity enhancement and relative intensity noise suppression, including a light source for emitting an optical signal. After the light source, a polarizer, a circulator, and a 50:50 coupler are sequentially arranged. A modulator for completing dual-polarization modulation is connected to the 50:50 coupler. A fiber optic loop is connected to the modulator. The optical signal can complete sensing inside the fiber optic loop and carry the Sagnac phase difference back to the modulator. A polarization beam splitter is also connected to the circulator. A horizontal photodetector and a vertical photodetector are respectively connected to the polarization beam splitter. The horizontal photodetector and the vertical photodetector transmit the converted electrical signals to an FPGA with an internal differential algorithm and a noise subtraction algorithm through cables.

[0006] A further improvement of the technical solution of the present invention lies in that the output end of the polarizer is fusion spliced with the input port of the circulator at 45 degrees through a polarization-maintaining optical fiber, and all the other optical components are connected by polarization-maintaining optical fibers.

[0007] A further improvement of the technical solution of the present invention lies in that the modulator specifically includes a first Faraday rotator and a second Faraday rotator with opposite rotation directions. A lithium niobate crystal is arranged between the first Faraday rotator and the second Faraday rotator. The two ends of the lithium niobate crystal are fusion spliced with the first Faraday rotator and the second Faraday rotator through polarization-maintaining optical fibers to ensure that the optical axes are aligned.

[0008] A further improvement of the technical solution of the present invention lies in that the internal optical path of the modulator is as follows: the vertically polarized light propagating clockwise is rotated 45 degrees clockwise after passing through the second Faraday rotator, and then vibrates along the y-axis of the lithium niobate crystal and propagates in the -z direction. After being rotated 45° counterclockwise at the first Faraday rotator, the light returns to the vertical direction after opposite rotation; the horizontally polarized light propagating clockwise is rotated 45 degrees clockwise after passing through the second Faraday rotator, and then vibrates along the x-axis of the lithium niobate crystal and propagates in the -z direction. After being rotated 45° counterclockwise at the first Faraday rotator, the light returns to the horizontal direction after opposite rotation; the vertically polarized light propagating counterclockwise is rotated 45 degrees counterclockwise after passing through the first Faraday rotator, and then vibrates along the x-axis of the lithium niobate crystal and propagates in the z direction. After being rotated 45° clockwise at the second Faraday rotator, the light returns to the vertical direction after opposite rotation; the horizontally polarized light propagating counterclockwise is rotated 45 degrees counterclockwise after passing through the first Faraday rotator, and then vibrates along the y-axis of the lithium niobate crystal and propagates in the z direction. After passing through the second Faraday rotator and being rotated 45° clockwise, the light returns to the horizontal direction after opposite rotation. The x-axis and y-axis of the lithium niobate crystal are both ordinary optical axes and have opposite responses to voltage.

[0009] A further improvement of the technical solution of the present invention lies in that the fiber optic gyroscope enables the orthogonally polarized light propagating in the polarization-maintaining optical fiber to present complementary responses with equal magnitudes and opposite signs to the same rotation speed through dual polarization modulation, and realizes sensitivity enhancement through a differential algorithm. At the same time, the relative intensity noise (RIN) that is the same and synchronous in the two polarization states is suppressed through a noise subtraction algorithm; in the differential algorithm, the modulation signal is selected as a sawtooth wave with an initial phase of -π / 2 and the phase difference corresponding to its voltage traverses from -π / 2 to 3π / 2. Then, P o1 and P o2 is

[0010]

[0011] wherein, ω mis the frequency of the modulation signal, and the output is a standard sine signal with the same frequency as the modulation signal. For the same angular velocity, Output 1 and Output 2 have complementary responses, and the sensitivity of the gyroscope can be doubled through differential operation.

[0012] A further improvement of the technical solution of the present invention lies in that: in the noise subtraction algorithm, in terms of noise suppression, the output signal can be divided into a signal part and a noise part The noise components caused by RIN in Equations (1) and (2) can be expressed as:

[0013]

[0014] After noise subtraction, the noise of the output signal is denoted as:

[0015]

[0016] where is a random function of time, representing the intensity fluctuation caused by RIN; when the IFOG is in a stationary state or in a small rotation state (i.e., Δφ s is close to zero), performing noise subtraction suppresses RIN.

[0017] A further improvement of the technical solution of the present invention lies in that: the modulation signal is selected as a sawtooth wave with an initial phase of -π / 2, and the phase difference corresponding to its voltage traverses from -π / 2 to 3π / 2.

[0018] Due to the adoption of the above technical solution, the technical progress achieved by the present invention is that: through dual-polarization modulation and differential algorithm, the sensitivity of the fiber optic gyroscope is effectively improved. Compared with the traditional fiber optic gyroscope, the sensitivity is doubled, and the carrier angular velocity can be measured more accurately. By using the noise subtraction algorithm, the relative intensity noise is effectively suppressed, the signal quality is improved, and the stability and reliability of the fiber optic gyroscope in complex environments are enhanced. It provides a theoretical and experimental basis for the further development of new high-performance IFOGs, and helps to expand the application of fiber optic gyroscopes in more fields such as high-precision navigation and inertial measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings;

[0020] Figure 1 is a schematic structural diagram of the fiber optic gyroscope of the present invention;

[0021] Figure 2 It is a schematic structural diagram of the modulator in the present invention;

[0022] Among them, 1 is a light source, 2 is a circulator, 3 is a circulator, 4 is a 50:50 coupler, 5 is a Faraday rotator I, 6 is a lithium niobate crystal, 7 is a Faraday rotator II, 8 is an optical fiber loop, 9 is a polarization beam splitter, 10 is a horizontal photodetector, 11 is a vertical photodetector, and 12 is an FPGA. Specific embodiments

[0023] The present invention will be further described in detail below in conjunction with embodiments:

[0024] As Figure 1 shown, it is a schematic structural diagram of a dual-polarization fiber optic gyroscope that realizes sensitivity enhancement and relative intensity noise suppression. The functions of each optical component are as follows:

[0025] The light source 1 is used to emit optical signals;

[0026] The polarizer 2 converts the light emitted by the light source into linearly polarized light;

[0027] The circulator 3, the linearly polarized light is incident on the circulator at 45°, and is decomposed into two polarized lights, horizontal and vertical;

[0028] The 50:50 coupler 4 splits the horizontal and vertical polarized lights into clockwise light and counterclockwise light respectively;

[0029] The Faraday rotator 5 rotates the polarization direction of the light.

[0030] The lithium niobate crystal 6 modulates the polarized light.

[0031] The Faraday rotator 7 rotates the polarization direction of the light.

[0032] The polarization-maintaining fiber loop 8 is used to complete sensing;

[0033] The polarization beam splitter 9 is used to decouple the horizontal and vertical polarized lights after passing through the coupler 4 and the circulator 3;

[0034] The horizontal photodetector 10 converts the decoupled horizontal polarized light into an electrical signal carrying angular velocity information;

[0035] The vertical photodetector 11 converts the decoupled vertical polarized light into an electrical signal carrying angular velocity information respectively;

[0036] The field programmable gate array (FPGA) 12 is used to implement signal processing processes such as differential sensitivity enhancement algorithms and demodulation algorithms; and all the optical devices are polarization-maintaining types.

[0037] The modulator 13 is asFigure 2 As shown, it is used to complete dual-polarization modulation. The modulator is constructed by inserting a lithium niobate crystal between two optical rotators with opposite rotation directions; both ends of the lithium niobate crystal 6 are fusion-spliced to the first Faraday rotator 5 and the second Faraday rotator 7 through polarization-maintaining fibers to ensure the alignment of the optical axes.

[0038] Optical path setup: Polarization-maintaining fibers are used to connect all optical components in sequence to ensure the alignment accuracy of the fibers during the connection process, reduce connection losses, and the connection relationship and placement positions are as Figure 1 shown. The specific connection relationship is:

[0039] Light source and polarizer: The light source 1 is located at the starting end of the system, and its output end is connected to the input end of the polarizer 2 through a polarization-maintaining fiber (PM Fiber). The unpolarized light emitted by the light source is converted into linearly polarized light by the polarizer, and the polarization direction is 45°.

[0040] From polarizer to circulator: The output end of the polarizer 2 is fusion-spliced to the input port of the circulator 3 at 45 degrees through a polarization-maintaining fiber. After the linearly polarized light is incident on the circulator at 45°, it is decomposed into horizontally polarized light (H) and vertically polarized light (V).

[0041] From circulator to 50:50 coupler: The output port of the circulator 3 is connected to the input end of the 50:50 coupler 4 through a polarization-maintaining fiber. The coupler splits the horizontally and vertically polarized lights into clockwise light (CW) and counterclockwise light (CCW) respectively, and the two beams of light enter the modulator 1-13 through the two output ports of the coupler.

[0042] Internal optical path of the modulator: The modulator 13 consists of two Faraday rotators 5 and 7 with opposite rotation directions and a lithium niobate crystal 6 in the middle. Clockwise light (CW) path: The horizontally polarized light (H-CW) rotates clockwise by 45° after entering the second Faraday rotator 7, vibrates along the y-axis direction of the lithium niobate, and propagates in the -z direction; the vertically polarized light (V-CW) rotates clockwise by 45° after entering the second Faraday rotator 7, vibrates along the x-axis direction of the lithium niobate, and propagates in the -z direction.

[0043] Counterclockwise light (CCW) path: The horizontally polarized light (H-CCW) rotates counterclockwise by 45° after entering the first Faraday rotator 5, vibrates along the x-axis direction of the lithium niobate, and propagates in the z direction; the vertically polarized light (V-CCW) rotates counterclockwise by 45° after entering the first Faraday rotator 5, vibrates along the y-axis direction of the lithium niobate, and propagates in the z direction.

[0044] The specific optical path is as follows: The vertically polarized light propagating clockwise is rotated clockwise by 45 degrees after passing through the second Faraday rotator 7, and then vibrates along the y-axis of the lithium niobate crystal 6 and propagates in the -z direction. After being rotated counterclockwise by 45° at the first Faraday rotator 5, the light returns to the vertical direction after the opposite rotation; The horizontally polarized light propagating clockwise is rotated clockwise by 45 degrees after passing through the second Faraday rotator 7, and then vibrates along the x-axis of the lithium niobate crystal 6 and propagates in the -z direction. After being rotated counterclockwise by 45° at the first Faraday rotator 5, the light returns to the horizontal direction after the opposite rotation; The vertically polarized light propagating counterclockwise is rotated counterclockwise by 45 degrees after passing through the first Faraday rotator 5, and then vibrates along the x-axis of the lithium niobate crystal 6 and propagates in the z direction. After being rotated clockwise by 45° at the second Faraday rotator 7, the light returns to the vertical direction after the opposite rotation; The horizontally polarized light propagating counterclockwise is rotated counterclockwise by 45 degrees after passing through the first Faraday rotator 5, and then vibrates along the y-axis of the lithium niobate crystal 6 and propagates in the z direction. After passing through the second Faraday rotator 7 and being rotated clockwise by 45°, the light returns to the horizontal direction after the opposite rotation. The x-axis and y-axis of the lithium niobate crystal 6 are both ordinary optical axes and have opposite responses to voltage.

[0045] Both ends of the lithium niobate crystal 6 are fusion spliced with the Faraday rotators 5 and 1-7 through polarization-maintaining optical fibers to ensure the alignment of the optical axes.

[0046] Modulator to fiber loop: The output end of the modulator 13 is connected to the polarization-maintaining fiber loop 8 through an optical fiber. Four optical signals (H-CW, V-CW, H-CCW, V-CCW) complete sensing in the fiber loop and carry the Sagnac phase difference back to the modulator.

[0047] Fiber loop to polarization beam splitter: The optical signal returns to the modulator 13 through the polarization-maintaining fiber loop 8. After passing through the rotators 5 and 7 and the lithium niobate crystal 6 again, the two optical signals are combined by a coupler and then output to the polarization beam splitter 9 through the circulator 3. The polarization beam splitter 9 decouples the horizontally polarized light (H) and the vertically polarized light (V) and outputs them to two horizontal photodetectors 10 and vertical photodetectors 11 respectively.

[0048] Photodetector to FPGA: The horizontal photodetector 10 and the vertical photodetector 11 convert the decoupled horizontally polarized light and vertically polarized light signals into electrical signals and transmit them to the FPGA 1-12 with built-in differential algorithm and noise subtraction algorithm through coaxial cables.

[0049] The fiber optic gyroscope enables the orthogonally polarized light propagating in the polarization-maintaining fiber to exhibit complementary responses with equal magnitudes and opposite signs to the same rotation speed through dual polarization modulation, and realizes sensitivity enhancement through a differential algorithm. At the same time, the same and synchronous relative intensity noise (RIN) in the two polarization states is suppressed through a noise subtraction algorithm. In the differential algorithm, the modulation signal is selected as a sawtooth wave with an initial phase of -π / 2, and the phase difference corresponding to its voltage traverses from -π / 2 to 3π / 2. Then, P o1 and P o2 are

[0050]

[0051] where ω m is the frequency of the modulation signal, the output is a standard sine signal and its frequency is the same as that of the modulation signal. For the same angular velocity, Output 1 and Output 2 have complementary responses, and the sensitivity of the gyroscope can be doubled through differential operation.

[0052] In the noise subtraction algorithm, in terms of noise suppression, the output signal can be divided into a signal part and a noise part The noise components caused by RIN in Equations (1) and (2) can be expressed as:

[0053]

[0054] After noise subtraction, the noise of the output signal is denoted as:

[0055]

[0056] where is a random function of time, representing the intensity fluctuation caused by RIN; when the IFOG is in a stationary state or in a small rotation state (i.e., Δφ s is close to zero), the execution of noise subtraction suppresses RIN.

[0057] After the optical path is built and configured and the above fiber optic gyroscope is obtained, the modulation signal is set: a sawtooth wave modulation signal with an initial phase of -π / 2 and a frequency in the range of 1 kHz - 10 kHz is generated by a signal generator. By adjusting the parameters of the signal generator, the phase difference corresponding to the modulation signal voltage accurately traverses from -π / 2 to 3π / 2. The modulation signal is loaded onto the electrodes of the lithium niobate crystal in the modulator through a wire to ensure the stability and accuracy of the modulation signal.

[0058] Then signal processing is carried out: after the photodetector converts the optical signal into an electrical signal, the signal is transmitted to the FPGA through a high-speed data transmission line. In the FPGA, the differential sensitivity enhancement algorithm is based on the formula p diff = p o1 - po2 Process the output signals of two polarization states to achieve enhanced sensitivity; the demodulation algorithm demodulates the electrical signals carrying angular velocity information to extract the angular velocity data of the carrier. At the same time, utilize the parallel processing ability of the FPGA to process a large amount of data in real time, improving the signal processing speed and accuracy.

[0059] The embodiments described above are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A dual-polarization fiber optic gyroscope for achieving sensitivity enhancement and relative intensity noise suppression, comprising a light source (1) for emitting an optical signal, characterized in that: A polarizer (2), a circulator (3) and a 50:50 coupler (4) are sequentially arranged behind the light source (1); a modulator (13) for completing dual polarization modulation is connected to the 50:50 coupler (4); an optical fiber ring (8) is connected to the modulator (13); the optical fiber ring (8) can sense the optical signal inside and carry the Sagnac phase difference back to the modulator (13); a polarization beam splitter (9) is also connected to the circulator (3); a horizontal photodetector (10) and a vertical photodetector (11) are respectively connected to the polarization beam splitter (9); the horizontal photodetector (10) and the vertical photodetector (11) transmit the converted electrical signal to an FPGA (12) with a built-in differential algorithm and a noise subtraction algorithm through a cable.

2. A dual-polarization fiber optic gyroscope for achieving sensitivity enhancement and relative intensity noise suppression according to claim 1, characterized in that: The output end of the polarizer (2) is fused at 45 degrees with the input port of the circulator (3) through a polarization-maintaining optical fiber, and the remaining optical components are connected with polarization-maintaining optical fibers.

3. The dual-polarization fiber optic gyroscope for achieving sensitivity enhancement and relative intensity noise suppression according to claim 1, characterized in that: The modulator (13) specifically comprises two Faraday rotators (1) (5) and (2) (7) with opposite rotation directions, a lithium niobate crystal (6) is arranged between the Faraday rotator (1) (5) and (2) (7), and two ends of the lithium niobate crystal (6) are fused with the Faraday rotator (1) (5) and (2) (7) via polarization-maintaining optical fibers to ensure that the optical axes are aligned.

4. The dual-polarization fiber optic gyroscope for achieving sensitivity enhancement and relative intensity noise suppression according to claim 3, characterized in that: The internal optical path of the modulator (13) is as follows: the vertically polarized light propagating clockwise is rotated 45 degrees clockwise after passing through Faraday rotator 2 (7), and then propagates in the -z direction along the y-axis vibration of the lithium niobate crystal (6), and after being rotated 45 degrees counterclockwise at Faraday rotator 1 (5), the light returns to the vertical direction after undergoing the opposite rotation; The horizontal polarized light propagating clockwise is rotated 45 degrees clockwise after passing through Faraday rotator 2 (7), and then propagates in the -z direction along the x-axis vibration of the lithium niobate crystal (6), and after being rotated 45 degrees counterclockwise at Faraday rotator 1 (5), the light returns to the horizontal direction after undergoing the opposite rotation; the vertical polarized light propagating counterclockwise is rotated 45 degrees counterclockwise after passing through Faraday rotator 1 (5), and then propagates in the z direction along the x-axis vibration of the lithium niobate crystal (6), and after being rotated 45 degrees counterclockwise at Faraday rotator 1 (5), the light returns to the horizontal direction after undergoing the opposite rotation. After rotating 45° clockwise at Faraday rotator 2 (7), the light returns to the vertical direction after undergoing the opposite rotation; the horizontally polarized light propagating counterclockwise is rotated 45 degrees counterclockwise after passing through Faraday rotator 1 (5), and then propagates in the z direction along the y-axis vibration of the lithium niobate crystal (6), and after rotating 45° clockwise at Faraday rotator 2 (7), the light returns to the horizontal direction after undergoing the opposite rotation. The x-axis and y-axis of the lithium niobate crystal (6) are both ordinary optical axes and have opposite responses to voltage.

5. The dual-polarization fiber optic gyroscope for achieving sensitivity enhancement and relative intensity noise suppression according to claim 2, characterized in that: The fiber gyroscope uses dual polarization modulation to make the orthogonal polarized light propagating in the polarization-maintaining fiber present complementary responses of equal magnitude and opposite sign to the same rotation speed, and realizes sensitivity enhancement through the differential algorithm. At the same time, the noise subtraction algorithm is used to suppress the same and synchronized relative intensity noise (RIN) in the two polarization states. In the differential algorithm, the modulation signal is selected as a sawtooth wave with an initial phase of -π / 2 and its voltage corresponding phase difference traverses from -π / 2 to 3π / 2. Then, P o1 and P o2 yes Among them, ω m is the frequency of the modulation signal. The output is a standard sinusoidal signal with the same frequency as the modulation signal. Output 1 and output 2 have complementary responses to the same angular velocity. The sensitivity of the gyroscope can be increased by two times through differential operation.

6. A dual-polarization fiber optic gyroscope for achieving sensitivity enhancement and relative intensity noise suppression according to claim 5, characterized in that: In the noise subtraction algorithm, in terms of noise suppression, the output signal can be divided into the signal part and the noise part The noise component caused by RIN in equations (1) and (2) can be expressed as: After noise subtraction, the noise of the output signal is recorded as: in, is a random function of time, representing the intensity fluctuations caused by RIN; when the IFOG is at rest or in a small rotation (i.e., Δφ s close to zero), performing noise subtraction suppresses RIN.

7. A dual-polarization fiber optic gyroscope for achieving sensitivity enhancement and relative intensity noise suppression according to claim 6, characterized in that: The modulation signal is selected as a sawtooth wave with an initial phase of -π / 2, and the phase difference corresponding to its voltage traverses from -π / 2 to 3π / 2.

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